Killed by self after successful trial by combat and other

He won his trial by combat by killing his liege Benjen and that resulted in him killing himself as well. I've also noticed that people who plot to murder other characters die upon successfully completing their plot. Death reason is the generic natural death. A strange recurring theme. Even using the murder command results in the murderer dying when it is successful.
edit:it seems the murderer dying isn't as consistent as I thought but it did happen multiple times.